The present invention relates to a switching power supply device. Specifically, the present invention relates to a switching power supply device in which standby power consumption can be decreased by remote control when an output voltage is in an OFF state.
A switching power supply device that has a power factor correction (PFC) circuit is known. The conventional switching power supply device is configured with the PFC circuit and a DC/DC converter circuit. Specifically, the PFC circuit corresponds to an AC/DC converter and improves a power factor. The DC/DC converter circuit stabilizes a direct current (DC) output voltage and isolates an input and an output thereof from each other.
Japanese Patent Publication No. 2001-314083 discloses a typical PFC circuit. Further, Japanese Patent Publication No. 2002-272107 discloses a typical DC/DC converter circuit. FIG. 6 shows a circuit diagram of a conventional switching power supply device 60 that is configured with the PFC circuit that is disclosed in Japanese Patent Publication No. 2001-314083 and the DC/DC converter circuit that is disclosed in Japanese Patent Publication No. 2002-272107. As shown in FIG. 6, in the conventional switching power supply device 60, an input voltage Vin that is generated by an AC power source is input to a rectifier circuit 3 that is composed of a diode bridge. Further, a voltage that is obtained by performing a full-wave rectification of the input voltage Vin through the rectifier circuit 3 is supplied to a step-up chopper circuit 62 of a PFC circuit 61. As a structure of the step-up chopper circuit 62, one output terminal of the rectifier circuit 3 is connected to one end of an inductor 63. Another end of the inductor 63 is connected to a drain of a field effect transistor (FET) 7 that corresponds to a switching element. Further, a source of the FET 7 is connected to another output terminal of the rectifier circuit 3. Further, a diode 9 and a smoothing capacitor 10, which are connected in series, are connected in parallel between the source and the drain of the FET 7. The PFC circuit 61 has a control unit 65 that stabilizes a DC voltage Vdc and improves a power factor by performing switching control of the FET 7. As discussed above, the PFC circuit 61 is configured with the step-up chopper circuit 62 and the control unit 65.
In the step-up chopper circuit 62, when the FET 7 is turned ON, energy is stored to the inductor 63 according to a current that is obtained by performing a full-wave rectification of the input voltage Vin through the rectifier circuit 3. On the other hand, when the FET 7 is turned OFF, the DC voltage Vdc, which is higher than a voltage that is input to the step-up chopper circuit 62 from the rectifier circuit 3, is generated between both ends of the smoothing capacitor 10 by overlapping the stored energy that is stored in the inductor 63 with a voltage that is generated between output terminals of the rectifier circuit 3. At this time, the DC voltage Vdc is smoothed by the smoothing capacitor 10.
The control unit 65 monitors the DC voltage Vdc that is smoothed by the smoothing capacitor 10 as a feedback signal and makes the DC voltage Vdc constant by controlling a pulse conduction width of the FET 7. Specifically, the control unit 65 performs the following control: the control unit 65 narrows the pulse conduction width of the FET 7 when the DC voltage Vdc increases as compared with a predetermined voltage that is a reference voltage. On the other hand, the control unit 65 widens the pulse conduction width of the FET 7 when the DC voltage Vdc decreases as compared with the predetermined voltage that is the reference voltage. Further, the control unit 65 improves a power factor by making a current waveform of a current that flows in the inductor 63 close to a voltage waveform as a sine wave of the voltage that is obtained by performing the full-wave rectification of the input voltage Vin through the rectifier circuit 3 by performing the switching control of the FET 7.
Further, as shown in FIGS. 6 and 7, the DC/DC converter circuit 70 disclosed in Japanese Patent Publication No. 2002-272107 is configured with a switching circuit 13 (shown in FIG. 7), a transformer 73, a rectifier circuit 15 (shown in FIG. 7), a smoothing circuit 16 (shown in FIG. 7) and a pulse width modulation (PWM) control unit 75. As the structure of the switching circuit 13, one end (positive (+) side) of the smoothing capacitor 10 of the step-up chopper circuit 62 is connected to one end of a primary side winding of the transformer 73. A drain of an FET 17 is connected to another end of the primary side winding of the transformer 73. Further, another end (negative (−) side) of the smoothing capacitor 10 of the step-up chopper circuit 62 is connected to a source of the FET 17. The switching circuit 13 is configured with the above structure.
Further, one end of a secondary side winding of the transformer 73 is connected to an anode of a rectifier diode 19. An anode of a freewheel diode 20 is connected to another end of the secondary side winding of the transformer 73. A cathode of the rectifier diode 19 and a cathode of the freewheel diode 20 are connected to each other. The rectifier circuit 15 is configured with the above structure. The smoothing circuit 16 is structured as follows. An inductor 21 and a smoothing capacitor 22 are respectively connected to each of the ends of the freewheel diode 20.
Further, the PWM control unit 75 monitors an output voltage Vo as a feedback signal and makes the output voltage Vo constant by controlling a pulse conduction width of a driving signal that is supplied to a gate of the FET 17.
In the DC/DC converter circuit 70, when the FET 17 is turned ON, the rectifier diode 19 is turned ON and the freewheel diode 20 is turned OFF because a voltage of a positive polarity is inducted at a terminal marked with a dot of the secondary winding of the transformer 73. As a result, the output voltage Vo is supplied to a load 100 through the rectifier diode 19 and the inductor 21. On the other hand, when the FET 17 is turned OFF, the rectifier diode 19 is turned OFF and the freewheel diode 20 is turned ON because a voltage is inducted to a terminal marked without a dot of the secondary winding of the transformer 73. As a result, the energy that is stored in the inductor 21 is supplied to the load 100 as the output voltage Vo.
Thus, in the DC/DC converter circuit 70, the voltage that is induced at the secondary winding of the transformer 73 by a switching operation of the FET 17 is rectified by the rectifier circuit 15 so as to make the output voltage Vo stable by the smoothing circuit 16.
Further, a switching power supply device that has the configuration as explained above in addition to an ON/OFF control function of the output voltage Vo (i.e., the ON/OFF corresponds to providing (being output) or Not-Providing (not being output) the output voltage) by a remote control has been known. FIG. 7 is a block diagram of a conventional switching power supply device 80 in which the ON/OFF control function of the output voltage Vo is realized by remote control. As shown in FIG. 7, in the switching power supply device 80, an external signal for the remote control is input to a control circuit 81 by performing an ON/OFF operation of an external signal ON/OFF circuit 85 that is provided outside. The ON/OFF operation of the external signal ON/OFF circuit 85 means that the external signal is or is not allowed to pass through toward the control circuit 81. Then, the control circuit 81 controls the PWM control unit 75. The PWM control unit 75 performs an ON/OFF operation for outputting a pulse signal that corresponds to a driving signal that is supplied to a gate of the FET 17 (shown in FIG. 6) of the DC/DC converter circuit 70. The ON/OFF operation for outputting the pulse signal as discussed above means that the pulse signal is or is not allowed to be supplied to the gate of the FET 17. As a result, the PWM control unit 75 controls the output voltage Vo of the DC/DC converter circuit 70.
A conventional remote control for the switching power supply device 80 is to externally perform ON/OFF control of the output voltage of the switching power supply device 80 while the input voltage Vin of the switching power supply device is applied. The ON/OFF control of the output voltage means that the output voltage is or is not output. The ON/OFF control of the output voltage is performed by controlling the DC/DC converter circuit 70. However, the PFC circuit 61, which improves a power factor by converting an AC voltage that corresponds to the input voltage Vin of the switching power supply device 80 into a DC voltage, keeps operating although the output voltage is in an OFF state (not output) by the remote control. Standby power consumption of the switching power supply device 80 that is controlled by the remote control is extremely large. This is because in spite of the OFF state of the output voltage by the remote control, the operation, i.e., converting the input voltage Vin to the output voltage, of the PFC circuit 61 is continued.
Accordingly, an object of the present invention is to provide a switching power supply device that can be realized as follows: in the switching power supply device that can control an ON/OFF operation for an output voltage Vo by remote control, the output voltage Vo can be stopped by an OFF operation through an external signal for the remote control while an input voltage Vin of the switching power supply device is applied. As a result, standby power consumption can be reduced. Resuming output of the output voltage Vo is stably performed by an external signal for the remote control.